There have been many attempts to achieve a liquid-tight, high-pressure seal arrangement for use in rotary valves. One such method is disclosed in U.S. Pat. No. 3,447,781, which teaches the use of an elastomeric seat ring for mating engagement against a seal member received in an annular groove in the valve body. That type seating structure is disadvantageous in that no metal-to-metal sealing can occur, such as is needed with fluids where corrosive or abrasive conditions are present.
One metal-seated ball valve uses precision machined surfaces to effect closure. That design can also cause unnecessary wear on the mating parts due to the flat mating seating surfaces. Because of the flat surfaces, any small particle in the flow stream such as sand may prevent proper contact of the mating surfaces, thereby creating an inherent potential for leakage. Also, such design of valve seat is excessively costly to manufacture.
Such disadvantages found in the prior art seating devices for rotary valves are overcome by the present invention which utilizes a thin, flexible metal seat ring mounted along one or both cylindrical ends to the valve body, or alternatively to the valve closure member, such as the ball in a rotary ball valve. The flexible metal seat ring is cantilevered on its opposite cylindrical end to the valve body and held against the valve's closure member by means of a resilient bias member, such as an elastomeric O-ring. The bias member is held captive in a pre-formed channel in the metal sea ring. Slotted fastener holes are formed in radially spaced locations in the flexible seat ring which, with associated threaded fasteners, permit automatic axial adjustment of the seat ring upon assembly and initial closure of the valve's closure member.
Importantly, during assembly of the pressure-assisted valve seating apparatus of the present invention, the fasteners holding the flexible seat ring are not tightened until the closure member has been moved to its full closed position. Advantageously, during assembly, the resilient bias member acts both as a spring to hold the flexible seating ring in place and also to radially locate that ring concentrically and evenly adjacent the ball's seat surface. Such a biasing action during assembly allows the flexible seat ring to move radially in selected areas to accommodate variations in the associated closure member. In effect, as the ball initially closes during assembly, each portion of the flexible seat ring moves axially and radially of the valve closure member's seat to find the ideal seated position. Thereafter, the flexible seat ring's fasteners are tightened to permanently lock the ring in place.
Advantageously, the cooperation of the spherical seat surface on the valve's closure member with the continuous flexible seat ring permits a relative forgiveness therebetween, thereby assuring closure of the valve to its true seating position. A valve made in accordance with the present invention cannot bind due to valve deflections, since the seating ring is in flexible contact with the closure member. Thus, expensive high precision, high torque valve actuators are not required. Rather, less costly standard actuators can be used in rotary valves having the flexible sealing structure of the present invention.
The present design can also be produced with eccentric action to the rotating closure member wherein the closure member lifts off of the flexible seating ring as it rotates to the open position thereby reducing seat wear. This is easily accomplished by offsetting the closure member's axis of rotation a nominal amount, such as by 1/4 inch.
Besides use in rotary ball valves, the pressure-assisted seating and sealing apparatus of the present invention can be used with other types of rotary valves, such as butterfly valves, for example.